On one of our cars the top radiator hose had a loose clamp where it attaches to the engine. I'm talking half a turn, not hanging off. That allowed a few drops out and onto the engine, but tightening it up solved the problem.

On my own MY99 the radiator end-tank went recently. The hole was too small for the naked eye but the coolant sprayed out on the left hand side (looking from the front). There was hardly any change in the coolant level and I only drove the 1 or 2km home at low speed after checking it very carefully. I could tell it was a very minor leak, not a gusher. When I got home I looked with a torch + the engine running and saw what looked like a needle going from the radiator to the engine, and I realised that was the coolant leaking out under pressure.

If the coolant hasn't been replaced recently is it possible a bit of gunk has temporarily blocked the hole from the inside?

I've only just fitted a new all-alloy Saber radiator (ebay spec, $200 delivered) and so far it's been great. I had a few dramas during the fitting process (fan holes not quite lined up, had to gently bend the small header-tank outlet upwards) but it's certainly working ok. I replaced the radiator hoses at the same time.

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Classic WRX all the way ...